Structural beams have been used in the construction of buildings and other structures for many years. It is well known that many applications of structural beams require the structural beams to support considerably large loads. One measure of expressing structural effectiveness of a beam is its strength-to-weight ratio, however, most solid metal beams do not have a favorable strength-to-weight ratio.
Further, the use of solid beams in many applications, e.g., in between a ceiling and vertically adjacent floor of multi-story buildings, requires additional space between the ceiling and floor to accommodate services such as air ducts, pipes, electrical conduits, and the like. Some builders have attempted to eliminate the need for the additional vertical space and accommodate the services by cutting away sections from the webs of the beams, and subsequently reinforcing the beams around the cut-away sections. However, this practice weakens the beams, requires expensive reinforcing, and does not permit the free relocation of such services.
Trusses have also been used in the construction of buildings and other structures for many years. However, trusses typically are comprised of many distinct pieces and may be labor intensive to assemble. In many cases, the labor cost to assemble a truss renders them impractical for many uses.
Castellated beams have been used to provide increased beam strength over traditional I-beams, channel shaped beams, and T-beams. Castellated beams mainly obtain their increased strength based on the principle that the resistance to loads depends to a great degree on the height of a beam, and that a beam with an increased height results in an increased load-carrying capacity.
Castellated beams are disclosed in U.S. Pat. Nos. 1,644,940, 2,002,044, 2,990,038, and 4,894,898. In these patents, an I-beam or a channel shaped beam is cut longitudinally along its web in a repetitive longitudinal pattern. Once the beam is cut, the beam halves are vertically separated and horizontally shifted one half the width of the pattern so that portions of the beam halves are aligned. The beam halves are then welded together along mating segments. The resulting structural beam includes spaced apertures with connecting segments located between the apertures. The shape of the apertures varies as a function of the shape of the cut.
One example of a prior art castellated beam is shown in FIGS. 1 and 2. In FIG. 1, an I-beam 10 having an upper flange 12, a web 14, and a lower flange 16 is cut longitudinally along its web 14 by a single cut 18 having a repetitive pattern to form two beam halves. The repetitive pattern cut 18 includes: (i) an upper horizontal segment 20, (ii) a downwardly and forwardly angled segment 22, (iii) a lower horizontal segment 24, and (iv) a upwardly and forwardly angled segment 26. The beam halves are then vertically separated and horizontally shifted. Upper and lower horizontal segments 20 and 24 are of equal length, while downwardly and forwardly angled segment 22 and upwardly and forwardly angled segment 26 are of equal length and equal but reversed slope. The beam halves are vertically separated by a distance 28 equal to the vertical spacing between upper horizontal segment 20 and lower horizontal segment 24. The beam halves are horizontally shifted by a distance 30 equal to one half the horizontal distance of the pattern, i.e., the horizontal distance between the beginning of upper horizontal segment 20 and the beginning of lower horizontal segment 24.
As shown in FIG. 2, the beam halves are then welded together along the interfacing horizontal segments 25 of the beam halves, i.e., the lower horizontal segments 24 of the upper beam half and the upper horizontal segments 20 of the lower beam half. The resulting beam structure 10' includes a vertically elongated web 14' with longitudinally spaced hexagonal apertures 34. However, the castellated beam 10' of FIG. 2 and the castellated beams of the aforementioned patents do not behave in a manner similar to a truss.
A tress, which is a structure known to provide exceptional strength, is defined by a geometry where the neutral axes of adjacent diagonals intersect at a common point substantially along the neutral axis of the chord member. Thus, for a structural beam to behave like a truss, the beam structure must transfer forces generally diagonally along connecting segments between top and bottom chords so that the neutral axes of adjacent connecting diagonal segments intersect at a point substantially along the neutral axis of a respective chord.
While the connecting portions of the FIG. 2 beam structure may possibly transfer forces diagonally, adjacent diagonal transfer axes 36, each approximated to intercept segment 25 at its center point and to be parallel to segment 26, intersect at a point 40 well outside the beam 10', and clearly, not substantially along the neutral axis 42 of the beam chord. Therefore, beam 10' can never fully behave as a truss and obtain the advantages associated therewith.
FIGS. 3 and 4 illustrate a beam structure as disclosed in Soviet Union Patent No. 1534-158. As depicted in FIG. 3, an I-beam 50 including upper and lower flanges 51 and 53 and a web 52, is cut along its web 52 in a longitudinally repeated trapezoidal-like pattern 54. The pattern of cut 54 includes: (i) a lower horizontal segment 56, (ii) an upwardly and rearwardly angled segment 58, (iii) an upper horizontal segment 60, and (iv) a downwardly and rearwardly angled segment 62. Cut 54 creates an upper beam half 63 having an upper chord 64 which includes upper flange 51 and the web portion which extends down to the longitudinal axis defined by upper horizontal segment 60. Similarly, a lower beam half 65 is created having a lower chord 66 which includes lower flange 53 and the web portion which extends up to the longitudinal axis defined by lower horizontal segment 56.
The resulting beam halves 63 and 65 include a respective chord 64 or 66 and trapezoidal shaped projections extending from the ends of chords 64 and 66. The trapezoidal shaped projections of upper beam half 63 are defined by an upwardly and rearwardly angled segment 58, a downwardly and rearwardly angled segment 62, a lower horizontal segment 56, and by a base at the bottom of upper chord 64 between adjacent upper horizontal segments 60. The trapezoidal shaped projections of lower beam half 65 are defined by an upwardly and rearwardly angled segment 58, a downwardly and rearwardly angled segment 62, an upper horizontal segment 60, and by a base at the top of lower chord 66 between adjacent lower horizontal segments 56.
Secondary cuts 70 are made in the trapezoidal projections to remove triangular sections 71 and to form forked sections 72 and 74. The ends of the forked sections 72 and 74 are parallel to the longitudinal axis of beam 50. As shown in FIG. 4, the bottom ends of forked sections 72 of upper beam half 63 butt against and are welded to forked sections 74 of lower beam half 65 along weld lines 76. The resulting beam 50' comprises diagonal joining members 78 formed from forked sections 72 and 74, and triangular shaped apertures 80 between adjacent diagonal joining members 78 and the inner extremities of chords 64 and 66.
However, structural beam 50' may be deficient in that stress concentrations can form dangerously close to various critical points at the intersection of chords and diagonals causing yield, instability or fatigue cracking which may precipitate the failure of the structure. A detailed view of adjacent diagonals 78 and their respective chord 64 is shown in FIG. 5. Point 82 is the panel point where the neutral axis 84a and 84b of diagonals 78a and 78b intersect, which may also fall along the neutral axis 86 of chord 64. Critical points 88, 89, and 90 exist where the edges of diagonals 78a and 78b meet chord 64.
While the structural deficiencies of beam 50' at critical points 88, 89, and 90 can be illustrated by various different stress distribution scenarios, only a single scenario is depicted herein. A single right-hand-side compressive force 92 would be resisted by: (i) a force 93 along neutral axis 86 of chord 64, (ii) a compressive force 94 along the neutral axis 84a of diagonal 78a, and (iii) a tensile force 95 along the neutral axis 84b of diagonal 78b. The resulting natural flow of forces, i.e. stress resultants from the diagonals 78a and 78b will approximately follow lines 96 and 97. As illustrated, the flows of stress resultants are located a short distance 98 from critical point 89 and a short distance 99 from critical point 90, causing the stresses in the vicinity of critical points 89 and 90 to be substantially increased. The location and magnitude of stress concentrations with respect to critical points 88, 89, and 90, prevent beam 50' from being used in other than primarily decorative applications.
There is a need, therefore, for a structural beam that will not only provide enhanced strength by increasing the height of the beam, but will also behave as a truss and reduce stress concentrations around critical points adjacent the panel points.